The lowdown on bead heads (excerpted from ESPN outdoors)
written by Jason Akl

To start to understand the importance of bead heads in fly patterns a quick look at the different type of beads used in fly patterns is a necessity.
Brass beads were specifically designed to add additional weight to fly patterns to help them get down deep, fast.
If you take a quick look into your fly box, what do you see? Do you have barrage of gold bead head nymph patterns lining your fly box or a run of the traditional weighted nymphs? In most cases, anglers probably carry a few of each and really never understand when, where, and why they should use one over the other. Bead head nymph patterns in recent years have come to the forefront in number of fish they fool all around the world. Fly anglers from north to south bet on the fact that if it swims in a river and is part of the trout or char family then can be caught on a bead head fly pattern.
To start to understand the importance of bead heads in fly patterns a quick look at the different type of beads used in fly patterns is a necessity:
1. Standard Drilled Gold/ Silver/ Nickel beads - These beads are the standard in the industry and have been worked into almost every famous bead head pattern available on the market. These beads are made exclusively for fly tiers using a "duel-diameter" hole. One small and one large bored-out hole to help slide easily around the hook bend and fit snuggly behind the hook eye. These beads are plated to resist tarnishing and provide flash even in the most stained of waters.
2. Coneheads -- These special brass bullet-shaped weights offer an exciting new way to weight flies. Instead of the traditional round shape, when using coneheads you are able to change the shape and profile of fly patterns.
3. Tungsten faceted Beads -- These unique products are relatively new to the market and weigh more than the traditional brass beads of equal size. The faceted face design helps reflect light in an irregular fashion.
4. Glass Beads -- Glass beads do not have the weight as compared to their metal counterparts, but add significant flash and color to nymph and wet fly patterns. Having a little lighter weight to these beads allow them to be incorporated in patterns that swim or get swung throughout the water column.
As winters grip lets loose over the landscape and the waters slowly warm, fish start to feed and do so ravenously. During these peak times the water's conditions are usually running fast and high, making getting flies down to fish difficult. There are many ways to get flies down to fish such as weighted lines and split shot on leaders, but the simplest answer to this problem is weight flies.
Brass beads were specifically designed to add additional weight to fly patterns to help them get down deep, fast. If you are crafty enough to tie your own flies, weighting the body of the hook shank with lead-free weight is a good start but will not always add enough weight to the hook shank to have the fly sink down to the bottom.
On standard bead heads there is one small and one large bored-out hole to help to slide it easily around the hook bend and fit snuggly behind the hook eye.
Although weighting the hook shank of a fly does make the fly heavier weighting the fly at its head region does more than just add weight. Forward loading a fly pattern like this serves two purposes. First off, to get the fly down deep; but secondly, to get the fly to sink head first. Having a pattern drop to the bottom head first will allow the fly to sink faster due to the fact that the fly is cutting through the current (the least amount of surface area perpendicular to the current). Coneheads are especially good for getting flies down to the bottom fast, seeing as the weight is more than traditional drilled beads. The specific cone head shape has an additional advantage, with its narrow front and wider rear the fly tends to become more weed-less bouncing off rocks and snags.
Furthermore, having a fly plunging towards the bottom head first more accurately imitates a swimming aquatic insect. Think to yourself, other than crayfish how many aquatic insects can you remember swimming backwards?
Lastly, the addition of weight to the forward section of flies will allow them to act as if they were a jig in the water with movement made to the fly line. Fly anglers cast these weight flies towards their target, allow them to sink and then will repeated short strips of line hop the beadhead fly along the bottom enticing fish.
Another major advantage of having bead heads incorporated into your favorite fly patterns is that they provide an element of flash to fly patterns by reflecting sunlight that has penetrated the water's surface. A trout's diet naturally consists of approximately 90 percent aquatic insects so anything that you can do to your favorite nymph pattern to help get the trout's attention will pay big dividends. When fishing bead head nymph anglers need to understand how fast a fly is going to sink. Experimenting with leader lengths and different sizes and types of beads will be needed to understand how fast the flies will sink. Using the countdown method after the cast will accurately let the fly angler know what level of the water column he or she is fishing. In most cases when presenting flies to fishing holding in deep holes the smaller more aggressive fish will strike the fly closer to the surface. Getting the fly down deep and rolling it along the bottom will improve your chances of hooking the real lunker in the hole.
One word of caution to fly anglers excited about getting out and using a bead head nymph this upcoming season is that the heavier the fly the harder it is to cast. A good idea is to shorten your leader when using beaded flies. A heavy leader, especially thick in the butt section will assist in casting, keeping the fly rolling smoothly above the level of your head. Moreover; picking the line off the water in a long horizontal plane and then casting forward at a vertical plane will not only help your casting, but also prevent the bead fly from coming into contact with your fly rod tip. Clipping the tip with a weighted fly will weaken or break the tip section.
As much as anglers love to see fish come up to the surface and explode on dry fly patterns, the chance to catch the real lunker in the rivers comes from drifting flies on bottom where these secretive giants lay. Adding bead heads to flies is a simple way to allow patterns to reach the fish's strike zone quickly and effectively plus the flash helps to get lethargic fish to take notice of what you're offering. Incorporating bead heads into your fly arsenal will take the guessing out of your next fly fishing adventure, while giving yourself the chance of landing that trophy fish of a lifetime.